I expect the only officially-supported language will be C, as that is what the SDK is written in. Other languages would need to be implemented as wrappers around that along with providing corresponding build toolchains, which is additional work that I suspect isn’t part of their version 1.0 target.
There are ongoing community efforts to do some of the work. I’m contributing to this Rust project; you can currently build external applications and use the Flipper Zero SDK directly via unsafe
code, but we are working to create safe Rust APIs for a nicer development experience.